EnergyEnergy

EnergyEnergy is the ability to is the ability to do work.do work.

Energy of motion is Energy of motion is called called kinetic energykinetic energy..

Energy unit is the Energy unit is the JouleJoule..

Kinetic energy = Kinetic energy = ½ x mass x ½ x mass x velocityvelocity22

KE = ½ mvKE = ½ mv22

If we have a mass of 2 and If we have a mass of 2 and a velocity of 3, what is the a velocity of 3, what is the kinetic energy?kinetic energy?

KE = ½ mvKE = ½ mv22

KE = .5 x 2 x 3KE = .5 x 2 x 322

KE =.5 x 2 x 9KE =.5 x 2 x 9 KE = KE = 99

KE = ½ mvKE = ½ mv22 is for kinetic is for kinetic energy in a energy in a straight linestraight line..

The The Work-Energy TheoremWork-Energy Theorem states that when work is done states that when work is done on an object, its kinetic energy on an object, its kinetic energy changes, and the work done changes, and the work done equals the change in kinetic equals the change in kinetic energy.energy.

Work = change in Work = change in kinetic kinetic energyenergy

Work = Work = KEKEff – KE – KEii

Since KE = ½mvSince KE = ½mv22 Work = Work =

½ m½ mffvvff22 – ½ m – ½ miivvii

22

If a 100 kg truck accelerates from If a 100 kg truck accelerates from 20 to 40 m /s. What work is done 20 to 40 m /s. What work is done by the engine?by the engine?

Work = ½ mWork = ½ mffvvff22 – ½ m – ½ miivvii

22

Work = ½ 100x40Work = ½ 100x4022 – ½ 100x20 – ½ 100x2022

Work=.5x100x1600 - .5x100x400Work=.5x100x1600 - .5x100x400 Work = 80,000 – 20,000Work = 80,000 – 20,000 Work = Work = 60,000 J60,000 J

Potential EnergyPotential Energy

Energy that is dependent Energy that is dependent upon height is called upon height is called potential energypotential energy..

Potential energy equation 1 Potential energy equation 1 = = mass x gravity x heightmass x gravity x height

Potential Energy = Potential Energy = PEPEPE = PE = mghmgh

Potential energy Potential energy equation 2 = equation 2 = weight x heightweight x height

PE = PE = whwh

A ball is thrown up. At the top A ball is thrown up. At the top of the path, how fast is the ball of the path, how fast is the ball moving?moving?

0 m/s – Not moving0 m/s – Not movingHow much kinetic energy How much kinetic energy

does the ball have at the top does the ball have at the top of the path?of the path?

0 – since it is not moving0 – since it is not moving

If the ball is thrown to a height of If the ball is thrown to a height of 5 meters and the ball has a mass 5 meters and the ball has a mass of 10 grams, what is the PE?of 10 grams, what is the PE?

Which equation? PE = mgh or Which equation? PE = mgh or PE = whPE = wh

PE = mghPE = mgh PE = 10 g x 10 m/sPE = 10 g x 10 m/s22 x 5 m/s x 5 m/s PE = PE = 500 J500 J

If gravity is the only force causing If gravity is the only force causing the potential energy, than the the potential energy, than the energy is called energy is called gravitational gravitational potential energypotential energy..

A system can also have potential A system can also have potential energy due to a energy due to a springspring..

Potential energy that is Potential energy that is stored in a spring is called stored in a spring is called elastic potential energyelastic potential energy..

The The equilibriumequilibrium of the of the spring is its unstretched spring is its unstretched position – where the spring position – where the spring has no force.has no force.

Equation for elastic potential Equation for elastic potential energy = ½ (spring constant) energy = ½ (spring constant) (spring displacement)(spring displacement)22

The spring constant is represented The spring constant is represented by by kk

The spring displacement or The spring displacement or distance the spring is stretched is distance the spring is stretched is represented by represented by xx

PEPEelasticelastic = = ½ kx ½ kx22

Spring constant of 180,000 and Spring constant of 180,000 and the spring is compressed .15 the spring is compressed .15 m, what is the elastic potential m, what is the elastic potential energy?energy?

PEPEelasticelastic = ½ kx = ½ kx22

PEPEelasticelastic = ½ 180,000 x .15 = ½ 180,000 x .1522

PEPEelasticelastic = ½ 180,000 x .0225 = ½ 180,000 x .0225PEPEelasticelastic = = 2025 J2025 J

As a mass accelerates on a As a mass accelerates on a spring, the spring’s stored PE spring, the spring’s stored PE is converted to is converted to kinetic energykinetic energy..

When the mass reaches the When the mass reaches the equilibrium position where x = equilibrium position where x = 0, the Potential energy = 0, the Potential energy = 00 and and the kinetic energy is at the the kinetic energy is at the maximummaximum..

The mass will continue to vibrate The mass will continue to vibrate back and forth, changing potential back and forth, changing potential energy to kinetic energy until the energy to kinetic energy until the mass mass stops movingstops moving..

This process with the mass This process with the mass vibrating right to left and back vibrating right to left and back again, changing kinetic to potential again, changing kinetic to potential and potential to kinetic is called and potential to kinetic is called simple harmonic motionsimple harmonic motion..

When potential energy is converted When potential energy is converted to kinetic energy, what forces take to kinetic energy, what forces take away some of the energy?away some of the energy?

Friction, - Energy is transformed Friction, - Energy is transformed into heatinto heat

The law of The law of conservation of conservation of energyenergy states that in an isolated states that in an isolated system, energy is conserved – it system, energy is conserved – it cannot be created or destroyed.cannot be created or destroyed.

Total energy 1 = Total energy 1 = PE + KEPE + KE

Total energy 2 = Total energy 2 = mgh + ½ mvmgh + ½ mv22

What is the total energy of a What is the total energy of a ball that has KE of 10 and PE ball that has KE of 10 and PE of 10?of 10?

Which Equation; TE = KE + PE Which Equation; TE = KE + PE or TE = ½ mvor TE = ½ mv22 +mgh? +mgh?

TE = KE + PETE = KE + PETE = 10 + 10TE = 10 + 10TE = TE = 2020

What is the total energy of a ball What is the total energy of a ball that has a mass of 250 and a that has a mass of 250 and a height of 25 with a velocity of 40?height of 25 with a velocity of 40?

Which Equation; TE = KE + PE or Which Equation; TE = KE + PE or TE = 1/2mvTE = 1/2mv22 +mgh? +mgh?

TE = ½mvTE = ½mv22 +mgh +mgh TE = ½ 250(40)TE = ½ 250(40)22 + 250(10)25 + 250(10)25 TE = ½ 250 (1600) + 250(10)25TE = ½ 250 (1600) + 250(10)25 TE=200,000+62,500 =TE=200,000+62,500 =262,500 J262,500 J